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losing outbound audio on FXO ports connected to IAD

We are using a UC500 with FXO ports for PSTN connection. On about 1 out of every 5 calls we are experiencing a loss of outbound audio, meaning we can hear the party on the far end but they can't hear us. In every case, the call starts out normally and we lose the audio after a few minutes of talking. Since we can't replicate the problem it is understandably hard to troubleshoot.

The only thing I can come up with is that our PSTN trunk lines are not "normal" analog trunks connected to a telco CO. We are using a CLEC that provides the analog trunks via an IAD and a dynamic voice/data service. Supposedly we have data access to a full T1 when no analog lines are in use and the data portion of the line is dynamically reduced when phone lines are in use. The IAD is an Adtran model. Should be configure the FXO ports differently for this setup?



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